Question

The numerical aperture of a step index fiber in (refractive index = 1), is 0.39. The diameter of the core is $200\mu \text{m}$.

The angle of acceptance when the fiber is used in water (refractive index = 1.33) is closest to

• A. ${16}^{\circ }$
• B. ${18}^{\circ }$
• C. ${17}^{\circ }$
• D. ${15}^{\circ }$

Answer 1

The correct option is C ${17}^{\circ }$

$A.A={\sin }^{-1}\left(\frac{N.A}{{\mu }_w}\right)({\mu }_w=\text{R.I. of water})$
$={\sin }^{-1}\left(\frac{0.39}{1.33}\right)\simeq {17}^{\circ }$